Zirconium tanning

ABSTRACT

TANNING OF ANIMAL HIDES AND SKINS BY SILICATE SODIUM ZIRCONIUM SULFATE AT A PH BETWEEN 1.0 AND 2.5 IS ACCELERATED WHEN THERE ARE PRESENT IN THE TANNING BATH AT LEAST FOUR SULFATE IONS PER ATOM OF ZIRCONIUM IN ADDITION TO THE SULFATE REQUIRED TO REACT WITH CATIONS PRESENT IN THE HIDES OR BATH WHICH FORM SPARINGLY SOLUBLE SULFATES.

United States Patent O 3,726,637 ZIRCONIUM TANNING Warren B. Blumenthal,North Tonawauda, N.Y., assignor to NL Industries, Inc., New York, N.Y.No Drawing. Filed Oct. 26, 1971, Ser. No. 192,636 Int. Cl. C14c 3/02,3/04 US. Cl. 8--94.25 4 Claims ABSTRACT OF THE DISCLOSURE Tanning ofanimal hides and skins by silicated sodium zirconium sulfate at a pHbetween 1.0 and 2.5 is accelerated when there are present in the tanningbath at least four sulfate ions per atom of zirconium in addition to thesulfate required to react with cations present in the hides or bathwhich form sparingly soluble sulfates.

BACKGROUND OF THE INVENTION The present invention relates to tanningwith soluble zirconium salts and is particularly concerned with theacceleration of tanning processes in which silicated sodium zirconiumsulfate is employed as the tanning agent.

It has been known for many years that solutions of zirconium salts canbe employed for tanning animal hides and skins. The resultant leather isdesirable because of its very light, substantially white, color which isof value as such and which also permits it to be dyed in clean pastelshades. In addition, leather tanned with zirconium salts does notcontinue to glow when, after ignition the flame is extinguished. In thisrespect it is different from and superior to chrome-tanned leather.Although various salts of zirconium have been suggested and used fortanning, silicated sodium zirconium sulfate, because of its relativelylow cost as compared to other zirconium tanning agents, is extensivelyemployed. The preparation of a silicated sodium zirconium sulfate isdescribed in Horrigan US. Pat. No. 3,096,143, granted July 2, 1963.

In the use of silicated sodium zirconium sulfate, however, it has beenfound that the tanning process often requires an inordinate length oftime to reach completion, particularly with thick hides and with hidesfrom older animals. This has been accepted as necessary by tanners butthe prolonged tanning time required has resulted in restriction of theuse of zirconium tanning because of the additional expense involved.Observation and study of zirconium tanning operations have revealed thatpenetration of the hide by the zirconium when silicated sodium zirconiumsulfate is used takes place at a moderate rate initially but graduallyslows down so that after about three or four hours further penetrationis extremely slow, with the result that several days may be required tocompletely tan a thick hide. Evidence has been found to support thebelief that the slowing down of the tanning process results fromextensive olation and condensation of zirconium species in the zirconiumtanning bath with resulting large molecules that do not penetrate thehide.

SUMMARY OF TI-H5 INVENTION It has been discovered that the time requiredfor thorough tanning when using silicated sodium zirconium sulfate asthe tanning agent can be greatly decreased, particularly when tanningthick hides, if a tanning bath is used which contains, per atom ofzirconium, at least four available sulfate ions, i.e. ions selected fromthe group of ions consisting of 80 and HSO4 As is well known, H80further ionizes to H+ and SO; The sulfate ions (this term hereinafterbeing intended to include both S0 and HSO4 can be provided from a numberof sources but, since the pH of the tanning bath is preferablymaintained in the range from about 1.0 to about 2.5, it is p CC usuallymost convenient to provide the sulfate ions by adding sodium bisulfate(NaHSOQ to the bath. This addition is preferably made substantiallysimultaneously with the addition of the silicated sodium zirconiumsulfate. Alternatively, the bath can be formed by adding silicatedsodium zirconium sulfate to a bisulfate solution. In any event, however,the addition of bisulfate to the bath should not be delayed once thesolution of silicated sodium zirconium sulfate has been prepared. By theterm available sulfate ions as used above is meant sulfate ions inaddition to the sulfate required to react with cations present in thehides or the bath which form sparingly soluble sulfates.

The preliminady hide treatment procedures, for example soaking,dehairing, lining, bating and pickling, may be conventional. On theother hand, zirconium tannage is quite tolerant as respects prior hidetreatment and in many cases modified preliminary treatment can be usedif desired. Subsequent to tanning and neutralization of the wet leatherto a pH of from about 3.0 to about 6.2, preferably about 3.5 to about6.0, the leather may be fat liquored and dried in accordance with wellknown procedures.

EMBODIMENTS The following examples illustrate the benefits of thepresent invention in tanning with silicated sodium zirconium sulfate.

Example 1 Using an experimental tanning drum, a piece of cattle hidehaving a limed weight of 4.77 kg. was, after washing and bating, tanned.To approximately 1200 ml. of water in the drum there was added 477 g. ofsodium bisulfate and 851 g. of silicated sodium zirconium sulfate andthe drum was run for five hours during which time the pH in the wheelrose from 1.1 to 1.7. Neutralization was then acomplished by slowlyadding to the drum 1750 ml. of a 5% solution of sodium hydroxide over aperiod of two hours. The tanned hide was left in the float overnight andthe next day, after addition of another 250 ml. of the sodium hydroxidesolution, the drum was run for an additional hour. The final pH of thetanned hide was found to be 5.8 and it had a shrinkage temperature ofover C. It was then drained, wrung, and split, the wet weight aftertrimming being 3.4 kg.

Example 2 Pieces of a salt cured green cowhide were soaked in water forrehydration. After conventional treatment including liming anddehairing, the pieces were washed and delimed and bated, using acommercial bate, in an experimental drum. The tanning was then carriedout, without removal of the bate solution, by adding to the drumsutlicient silicated sodium zirconium sulfate to provide 2% soluble ZrOand six mols of sodium bisulfate. Drumming was continued for about sixhours and was followed by neutralization with sodium bicarbonate to a pHof 3.23. A sample of leather taken after neutralization was found tohave a shrinkage temperature of 91 C.

Example 3 Twenty-three pounds of green calfskin which had been putthrough conventional beamhouse procedures was placed in an experimentaldrum with a float containing suflicient silicated sodium zirconiumsulfate to provide 6% soluble ZrO and 12% of sodium bisulfate. Afteroperation of the drum for three hours, the pH of the hide was raised to3.1 with sodium carbonate. The thus neutralized leather was found tohave a shrinkage temperature of 91.5 C. and inspection showed nountanned streaks or layers.

3 Example 4 Eight sides of brine-cured, fleshed cattle hide were givenconventional washing, soaking and liming beamhouse processing. Thewashed sides were then placed, in a large drum, in a 25% floatcontaining 1% ammonium persulfate and a commercial enzymatic batecontaining the equivalent of 2% enzyme. After running the drum for 30minutes, silicated sodium zirconium sulfate in an amount calculated toprovide 5% soluble zirconium, and sodium bisulfate were added anddrumming was continued for five hours. The pH of the leather wassubsequently adjusted to 3.5 with sodium bicarbonate. Tannage wasobserved to be complete and the leather was white with a shrinkagetemperature of 93 C.

The following example illustrates the deleterious effect of aging on thetanning efiectiveness of a silicated sodium zirconium sulfate bath.

Example 5 (a) Using an experimental drum, a beamhouse-processed hide wasdrummed for six hours in a tanning bath containing an amount ofsilicated sodium zirconium sulfate calculated to provide 6% soluble ZrOand 12% sodium bisulfate. The bath had been aged for a number of hoursafter preparation and before introduction of the hide. Afterneutralization, the hide was found to be well tanned.

(b) Using the same drum, a closely similar hide was drummed for sixhours in a bath containing the same amount of silicated sodium zirconiumsulfate as in (a) above, the bath after preparation having been aged forthe same time as in (a) above. No sodium bisulfate or other source ofadditional sulfate ions was, however, present. After the six hourdrumming period and neutralization, it was found that when soaked inwater long enough to remove the salt content thereof, the hide was nottanned as evidenced by its having the same shrinkage temperature as theuntanned hide.

Tanning can in some cases be carried out with an amount of silicatedsodium zirconium sulfate as low as about 2% (calculated as solubleZ102). Ordinarily, however, high quality tannage requires about 5% to 6%of soluble ZrO Additional tanning agent may, of course, be employedsince the tanning process may thereby be accelerated and the leatherobtained may be tougher and more opaque because of zirconium dioxidedeposited therein.

Since silicated sodium zirconium sulfates furnish sulfate ions, only theadditional sulfate ions required for the process of the invention needbe provided from another source. The most convenient source is believedto be sodium bisulfate although other materials such, for example, assulfuric acid, ammonium bisulfate, or normal sodium sulfate may be used.In general, such other sources are not as desirable as sodium bisulfatesince they will usually require a pH adjustment of the tanning bath toobtain the desired pH range for tanning. It is of great impor tance,however, for optimum results, that there be enough sulfate ions presentin the bath to provide at least four such ions for each zirconium atompresent, after allowing sulfate ions sufncient to react with cationspresent in the hide and/or the bath which form sparingly solublesulfates. Sulfate ions in excess of those necessary for cations thatform sparingly soluble sulfates and the four for each atom of zirconiummay be present in the bath if care is taken to maintain the pH of thebath in the desired range. On the other hand, when there are fewer thanthe ideal number of sulfate ions present, the overall acceleratingeffect on the tanning process is diminished, but some efiect is stillobservable if sulfate ions are present in substantial amounts. Thesituation is then tantamount, for operational purposes, to providingfour available sulfate ions for only some of the zirconium atomspresent.

Obviously, many modifications of and variations from the proceduredescribed in the foregoing examples are possible. The tolerance ofzirconium tannage for other materials has been mentioned above. Suchtolerance, for example, permits the addition of the tanning agent to thehate without intermediate washing as illustrated in Examples 2 and 3,and thus savings of time and water can be obtained.

It will be understood that the present novel tanning process can beemployed not only with calfskins and cattle hides, but also with otheranimal hides and skins such, for example, as horse hides and sheepskins. Consequently, the term hides herein is intended to include bothhides and skins and the term leather includes both tanned hides andtanned skins.

Percentages set forth herein are percentages by weight and thepercentages of materials comprised in the tanning bath are based on thewhite weight of the hide or hides being tanned.

What is claimed is:

1. A processfor tanning an animal hide which comprises treating suchhide with an aqueous tanning bath comprising silicated sodium zirconiumsulfate, while maintaining the pH of said bath between 1.0 and 2.5, saidbath containing sufiicient silicated sodium zirconium sulfate to provideat least 2% soluble ZrO therein and containing sufficient solublesulfate to provide, in solution, at least four sulfate ions per atom ofzirconium in said bath in addition to sulfate ions required forformation of sparingly soluble sulfates of other cationic elementspresent in said hide and/ or bath, and neutralizing said hide to a pH offrom about 3.0 to about 6.2.

2. A process as set forth in claim 1 in which said bath contains about5% to 6% soluble ZrO;,.

3. A process as set forth in claim 1 in which at least a portion of saidsoluble sulfate is provided by sodium bisulfate.

4. A process as set forth in claim 2 in which at least a portion of saidsoluble sulfate is provided by sodium bisulfate.

References Cited UNITED STATES PATENTS 3,096,143 7/1963 Horrigan 894.25

GEORGE F. LESMES, Primary Examiner W. R. DIXON, Assistant Examiner U.S.Cl. X.R. 252-857

